1.Field of the Invention
This invention relates to a process for removing soluble metallic salts from phosphate ester functional fluids, and in particular to a process for the reclamation of phosphate ester functional fluids.
2. Description of the Prior Art
Many functional fluid systems, such as cooling systems, lubricating systems, hydraulic fluid systems, heat transfer systems, and in particular gas turbine lubricating systems, utilize synthetic phosphate esters, particularly triarylphosphates, as the functional fluid. Triarylphosphates and their use as functional fluids are described in: U.S. Pat. No. 2,071,023 to Bass; U.S. Pat. No. 2,938,871 to Matuzzak; U.S. Pat. No. 3,012,057 to Fierce et al; U.S. Pat. No. 3,071,549 to Stark; U.S. Pat. No. 3,468,802 to Nail; U.S. Pat. No. 3,576,923 to Randall et al; U.S. Pat. No. 3,723,315 to Sullivan; U.S. Pat. No. 3,780,145 to Malec; U.S. Pat. No. 3,931,023 to Dounchis; and U.S. Pat. No. 3,992,309 to Dounchis. The entire disclosures of all of the aforementioned patents are incorporated herein by reference.
Generally, after use, phosphate ester functional fluids are discarded or, if attempts are made to reclaim such functional fluids, such attempts are generally ineffective and crude.
Generally, the used functional fluids are contaminated with undesirable metallic salts, such as copper, zinc, magnesium, tin, and iron, salts or mixtures thereof and have an acid number which is too high. Additionally, the used functional fluids contain water, mineral oils and solid contaminants. The combination of soluble metallic salt contamination and high acid number causes corrosion of metallic parts in contact with the functional fluid and autocatalytic oxidation of such metallic parts. Additionally, the soluble metallic salts, for example, copper and zinc, can function as a catalyst in the decomposition of the fluid, particularly at elevated temperatures.
U.S. Pat. No. 3,706,822 issued Dec. 19, 1972 to Caldwell and Sorrell describes a process for refining crude organophosphorus esters comprising washing the ester with a water or aqueous lye solution containing an agent capable of inhibiting the formation of metal ion/partial ester complexes during said washing. These agents include certain chelating agents, and in particular ethylenediaminetetraacetic acid and the sodium, potassium and calcium salts thereof. This refining process, however, is accomplished in an aqueous solution. Such a process applied to the reclamation of used functional fluids would require process steps and equipment to remove the water, for a functional fluid must be substantially free of water.